Krill is a small crustacean which lives in all the major oceans world-wide.
Krill can be found in the Pacific Ocean (Euphausia pacifica), in the Northern Atlantic (Meganyctiphanes norvegica) and in the Southern Ocean off the coast of Antarctica (Euphausia superba). Krill is a key species in the ocean as it is the food source for many animals such as fish, birds, sharks and whales. Krill can be found in large quantities in the ocean and the total biomass of Antarctic krill (E. superba) is estimated to be in the range of 300-500 million metric tons.
Krill has developed an efficient enzymatic digestive apparatus resulting in a rapid breakdown of the proteins into amino acids. Therefore, in order to prevent the degradation of krill the enzymatic activity is either reduced by storing the krill at low temperatures or the krill is made into a krill meal. During the krill meal process the krill is cooked so that all the active enzymes are denatured in order to eliminate all enzymatic activity. Krill is rich in phospholipids which act as emulsifiers. Thus, it is more difficult to use mechanical separation methods to separate water, fat, and proteins from krill oil, than it is in a regular fish meal production line. In addition, krill becomes solid, gains weight and loses liquid more easily when mixed with hot water. Eventually this may lead to a gradual build-up of coagulated krill proteins in the cooker and a non-continuous operation due to severe clogging problems. In order to alleviate this, hot steam must be added directly into the cooker. This operation is energy demanding and may also result in a degradation of unstable bioactive components in the krill such as omega-3 fatty acids, phospholipids and astaxanthin.
Traditional krill meal processing on board, in some factory vessels, produces only a small amount of krill oil. This krill oil is usually enriched in neutral lipids with very low or undetectable amount of phospholipids (0.5%). Normally, during the traditional on board krill process, fresh krill is heated using an indirect heating cooker with rotating screw conveyor, followed by a twin-screw press and drier. The press liquid obtained by the twin-screw press is passed through a decanter to remove the insoluble solids. The clarified decanter liquid is then used to feed separators centrifuges to separate the krill oil normally enriched with neutral lipids and astaxanthin. In this traditional process the phospholipids are bound to the proteins in the press cake, or krill meal.
US Patent Application Publication No. 20140107072 (which is hereby incorporated by reference) discloses a method for making krill meal using a two-step cooking process. In the first step the proteins and phospholipids are removed from the krill and precipitated as a coagulum. In the second stage the krill without phospholipids are cooked. Following this, residual fat and astaxanthin are removed from the krill using mechanical separation methods.
Typically, krill oil contains salt and trimethylamine N-oxide (TMAO), a natural and nontoxic substance. High TMAO levels in polar fishes and crustaceans are thought to increase osmotic concentration, thus depressing the freezing point of the body fluids. Odor is one of the most important parameters used to evaluate fish and fish oil freshness. Volatile amines such as ammonia and TMA, a degradation product of TMAO, are the characteristic molecules responsible for the fishy odor and flavor present in fish oils. Thus, TMAO is a precursor to TMA and as such must be removed from krill oil or krill oil extract to maintain the krill oil as an acceptable product which is fit for human consumption.
US Patent Application Publication No. 20140065236 discloses a solvent free process for obtaining phospholipids and neutral lipids enriched krill oils containing DHA and EPA poly-unsaturated fatty acids and astaxanthin. The process includes cooking fresh krill at high temperature-without agitation and or grinding; decanting the cooked krill for obtaining a partial de-fatted and de-watered solid and a liquid; squeezing the obtained solid to obtain a press liquid and a solid fraction; centrifuging the press liquid to obtain the phospholipids enriched krill oil; centrifuging of the decanter liquid obtained to obtain the neutral lipid enriched krill oil and stick water. Stick water is a viscous quickly decomposing, and evil-smelling liquor that is obtained as a by-product in the wet process of manufacturing krill meal and krill oil by cooking the krill with steam and pressing and that is often concentrated by evaporation for use in animal feeds as a source of vitamins and amino acids.
Krill meal is a biomass composed of lipids, carbohydrates, and proteins. The krill meal is extracted in a solvent extraction process typically using ethanol as a solvent to remove proteins and free carbohydrates to provide a krill oil extract. The solvent used is typically food-grade quality. Following solvent extraction, the defatted krill meal and the ethanol oil solution are separated by physical means such as filtration or centrifugation. The recovered krill oil extract comprises neutral lipids, polar lipids, and astaxanthin.
Current production of high phospholipid krill oil is exemplified by the Aker BioMarine process. The Antarctic krill used in the production of SUPERBA Krill Oil (Available from Aker BioMarine AS, Oslo, NO) are naturally occurring organisms harvested in the wild. The harvested Antarctic krill is cooked and dried on the vessel to prepare krill meal. The krill meal is subjected to a solvent extraction process with ethanol as the solvent to remove proteins and free carbohydrates and provide an ethanol oil solution comprising the extracted oil and ethanol. Following extraction, the defatted krill meal and the ethanol oil solution are separated in a conventional manner. The ethanol-oil solution is then concentrated by evaporation. The ethanol-oil solution comprises ethanol, neutral and polar lipids, and astaxanthin. The ethanol-oil solution is clarified by centrifugation and the clarified ethanol solution is evaporated to provide a krill oil product. See “Krill Oil GRAS Notification-SUPERBA™ Krill Oil extracted from Antarctic krill, Euphausia superba”, (Submitted to US Food and Drug Administration, December 2010).
Krill oil and krill oil extract produced in the manner described hereinabove does not recover high yields or high purity of astaxanthin and the high phospholipid krill oil produced is only a portion of the phospholipids in the krill meal. Methods are sought to improve the recovery of high phospholipid krill oil, krill oil components, and astaxanthin without subjecting the oils to chemical and physical conditions which would result in degradation and which can reduce the overall recovery of these valuable components.